GHSA-2823-qmq8-rwvj: vLLM: Loose `cache_salt` validation lets a single request kill EngineCore on LMCache-MP deployments — uncaught downstream `ValueError` denial of service

```json { "summary": "vLLM (an AI serving framework) accepts a `cache_salt` parameter from users but validates it too loosely—only checking that it's a non-empty string. When LMCache-MP (a caching connector) is enabled, this value gets passed to a stricter validator that rejects strings containing special characters like `/`, `@`, `\`, or null bytes, or longer than 128 characters. If an invalid string is sent, the resulting error crashes the entire engine process instead of just failing that o